Ureaplasma-induced impairment of alveolar epithelial Na+ transport and its underlying mechanism.

<bold>Ureaplasma</bold> infection has been associated with adverse pulmonary short- and long-term outcome in preterm infants. Knowledge of underlying mechanisms is scarce. Epithelial Na⁺ transport is crucially involved in alveolar fluid clearance (AFC) at birth. Whether <italic>Ureaplasma</italic> colonisation of immature lungs impairs AFC is yet unknown. We aimed to determine pathomechanisms of <italic>Ureaplasma</italic>-driven lung morbidity. Rat fetal distal lung epithelial (FDLE) cells were incubated either with viable <italic>Ureaplasma</italic> for 24h or NH₃ versus NaOH, followed by analyses of Na⁺ transport in Ussing chambers, and Western blots. The urease inhibitor flurofamide was used to prevent bacterial NH₃ production. Ureaplasma strongly reduced Na⁺ transport in FDLE cells due to inhibition of the epithelial Na⁺ channel (ENaC). <italic>Ureaplasma</italic> infection also shifted pH levels above 8.0 within 24h. Exposure of FDLE cells to NH₃ at pH 8.0 strongly reduced Na⁺ transport and ENaC activity, while NaOH-driven pH shift lacked this effect. Moreover, phosphorylation of ERK, a signalling molecule diminishing ENaC activity, was increased by <italic>Ureaplasma</italic>. This finding was reproduced by NH₃ incubation, but not by NaOH at pH 8.0. Flurofamide prevented the <italic>Ureaplasma</italic>-induced reduction of Na⁺ transport, further supporting a contributing role of NH₃ production to the impaired ENaC activity. Notably, flurofamide also prevented ERK phosphorylation induced by <italic>Ureaplasma</italic>. Reduction of Na⁺ transport reveals a potential mechanism of <italic>Ureaplasma</italic>-driven lung disease in preterm infants. We identified NH₃ as an <italic>Ureaplasma</italic>-driven agent responsible for the inhibition of Na⁺ transport, and flurofamide as a counteragent preventing NH₃ production by urease inhibition.